1. Field of the Invention
This invention relates to printers and, in particular, to systems and methods for monitoring toner consumption in printing devices.
2. Description of the Related Technology
Even with the increasing use of the Internet, email and digital media, the volume of printed matter produced by businesses continues to rise. Millions of tons of imaging material, such as toner, is consumed in the United States each year. Furthermore, printing purchases make up a significant percentage of corporate expenditures, and downtime due to broken printing devices or waiting for replacements of empty toner cartridges can add to these expenses.
In view of the foregoing, several systems and methods have been developed for measuring toner consumption. Conventional methods for measuring toner consumption may be classified into two general categories. The first category of toner measurement methods utilizes a mechanical switch that monitors the physical level of the toner in the cartridge. When the toner drops below a predetermined level, the switch closes, resulting in a “low toner” signal being transmitted to a user interface of the printer or to a remote location via network protocols. A major drawback of this first category is that there is no measurement of toner consumption available to the user until the toner actually reaches a low level. For example, the user is not informed of progressive levels of consumption, such as when there is 75% or 50% of the toner remaining.
The second category of toner measurement methods utilizes a page pixel count from the image data sent to the printer. In general, the number of pixels on a particular page is an indication of the amount of toner used for that page. Such mapping of page pixel count to toner usage also allows for continuous monitoring of toner consumption and for providing a “gas gauge” of the toner to the user.
The relationship between pixel count and toner consumption, however, is not linear. Rather, due to a “diffusion effect,” images having the same number of pixels, but having different positioning of pixels, consume different amounts of toner. For example, the amount of toner used to print a number of pixels that are positioned next to each other is generally less than the amount of toner used to print the same number of pixels dispersed throughout a page. To address this diffusion effect, at least one system includes logic for counting the number of pixel transitions (i.e., laser on to laser off, laser off to laser on) per scan line for a particular image. The system then uses a ratio of the transition count to the pixel count to estimate the toner consumption for the particular image.